Oh yeah, a 12 gauge slug could easily deliver enough blunt force trauma to be deadly even if it never penetrated. At the very least it would be incapacitating.
Liberals are forever getting tangled up in webs of unintended consequences. It's a result of their static view of the world. They think they can tinker with people's lives and somehow it won't encourage compensating action elsewhere. One consequence of the 10 round magazine limit from 1994-2004 was the birth of the pocket rocket. One of the main benefits of the 9mm was its compactness, allowing a pistol to hold a lot of rounds. With that advantage artificially removed, people gravitated to larger and more powerful rounds. If the limit was going to be 10 rounds regardless, might as well make those 10 rounds as powerful as possible. So you started seeing rounds like the .45 in smaller platforms than ever before.
Likewise the so called "assault rifle". Their main advantage is capacity and controllability. They aren't even remotely "high powered", not compared with grandpaw's old .30-06 deer rifle. If this new ban goes into effect, it will generate renewed interest in classic rifle calibers. Those classic rifle calibers can slice through a vest like a hot knife through butter. Only the most cumbersome and impractical armor can reliably stop rounds like that.